KISSIMMEE — Just off the shore of Lake Tohopekaliga, Greg Zuhl reaches into the dark waters and comes up with a handful of rotting water plants, black and smelly. Most of the bottom of this part of the lake is covered with decaying vegetation, says Zuhl, a biologist with the Florida Game and Fresh Water Fish Commission. When the lake bottom is covered with muck, it is ruined for the fish that breed and eat there.

A drawdown is scheduled for next year that will lower the lake level and allow the muck to dry out. The commission also plans to scoop the rotten vegetation off the bottom and haul it away.

Before area sewage plant operators began dumping effluent into Lake Tohopekaliga, it was flanked by white sandy beaches, and the water was pristine -- clean enough for swimming.

Beginning in the early 1950s, sewage operators began dumping treated sewage into the waters. The nutrient-rich water stimulates plant life, clouding the water and leading to thick lake bottom buildup.

It has continued for 30 years. Today, four sewage plants pump 27.5 million gallons of effluent into the lake daily, 8 billion gallons yearly.

State regulatory agencies have ordered sewage plant operators to stop dumping effluent into the lake.

Some biologists question whether even that effort can restore the lake to the way it was before man invaded its shores.

''Some of the old timers will tell you that you used to be able to swim, and see the bottom of the lake,'' said Ed Moyer, a biologist with the Game and Fish Commission. ''I don't believe it will ever return to that state.''

Jim Hulbert, chief biologist with the Department of Environmental Regulation, agrees. He said it will be many years before all the effluent is flushed out of the lake. Even when it is gone, stormwater runoff from lawns, groves and pastureland will continue to fertilize the lake.

With a reputation as one of the best spots for bass fishing in the south, Lake Tohopekaliga draws thousands of anglers each year. It also pumps more than half a million dollars into the local economy annually, according to Game and Fish Commission figures.

The muck on the lake bottom has caused a sharp decline in the number of fish, biologists say. Fish cannot lay eggs in muck.

To save Lake Tohopekaliga from the plants that have killed other lakes in Central Florida, the cities of Orlando, Kissimmee and St. Cloud are spending millions of dollars to dispose of their effluent over land, where the soil filters it clean.

More than 90 percent pure, the phosphorus- and nitrogen-rich effluent is practically clear, experts say. But it is the quantity of phosphorus and nitrogen in the water that overstimulates plant growth and adversely affects the lake.

Last year, the lake absorbed about 35 tons of phosphorus and 450 tons of nitrogen, according to Game and Fish data.

Biologists are quick to point out that all four sewage plants have done an excellent job of cleaning up effluent over the last five years. Special processes used in Orlando and Kissimmee plants, and adjustments to the St. Cloud process, have sharply decreased the amount of phosphorus going into the lake.

In 1982 the effluent pumped daily into the lake contained 328 pounds of phosphorus. Today, about 130 pounds is poured into Lake Tohopekaliga daily.

The most improved sewage plants are the Orlando plants, which pour their effluent into Shingle Creek. The creek empties into the northern part of the lake, which has experienced a 70 percent reduction in phosphorus levels.

The two Orlando plants send 22 million gallons of effluent, containing 104 pounds of phosphorus, into the lake daily.

The most phosphorus-laden effluent comes from the St. Cloud plant, which is about four times as potent as the Kissimee and Orlando plant effluent.

Although the St. Cloud plant turns out 1 million gallons of effluent daily -- less than half of what Kissimmee produces -- it puts 17 pounds of phosphorus into the lake daily. The Kissimmee plant empties 9 pounds.

Some city officials argue that reducing effluent won't stop all the nutrients because runoff from fertilized lawns and pasturelands flows into the lake.

But Zuhl said the commission has seen a decrease in phosphorus levels in the lake that correlates to the decreases in effluent potency.

Near the St. Cloud Canal, where St. Cloud dumps its effluent, the water hyacinths grow extremely thick, and phosphorus levels there are among the highest in the lake, he said.

Water hyacinths are the chief nuisance water plant on the lake, Zuhl said. It is a fast-growing, leafy plant that thrives on phosphorus.

The hyacinths grow like a cancer on the lake. They choke out two plants that are a haven for fish because they supply food and a sheltered spawning area: panicum, a short, grassy plant, and bulrush, a taller grass-like plant. Both grow in shallow water.

Both plants are firmly rooted to the bottom and do not die in the winter, so they deposit little sediment on the bottom of the lake, Zuhl says.